Late Heavy Bombardment

Period between ~4.0 to 3.8 Ga ago when the Moon and other objects in the Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. were pounded heavily by wayward asteroids. The evidence for the Late Heavy Bombardment (LHB) includes the lunar mariaBroad low plains surrounded by basin-forming mountains, originally thought to be a sea (pl. maria). This term is applied to the basalt-filled impact basins common on the face of the Moon visible from Earth.   Click on Term to Read More basins and similar structures elsewhere, such as the Caloris Basin on Mercury and the great craters in the southern hemisphere of Mars. On Earth, LHB would have produced 22,000 or more impact craters with diameters >20 km, ~40 impact basins with diameters ~1000 km, and several impact basins with diameters ~5,000 km with a serious environmental damage event occurring about every 100 years. However, plate tectonics and erosionRemoval of weathered rocks by moving water, wind, or ice. Click on Term to Read More have erased the evidence from Earth’s surface. Conclusive evidence that Earth experienced LHB was not discovered until 2002, when British and Australian researchers announced they had found Tungsten (W) isotopes in 3.7 Ga rocks from Greenland and Canada that can only be extraterrestrial. Recent computer models also suggest that resonances and perturbations caused by the four large outer planets settling into their current orbital configurations would cascade large volumes of asteroidal material into the inner solar systemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with.